The objective is to understand the enzymology and regulation of the phosphoprotein phosphatases involved in the activation of glycogen synthase in skeletal muscle. Bifunctional protein cross-linking reagents and immunoprecipitation techniques would be used to establish the subunit structure of the glycogen-bound high molecular weight phosphatase. The relationships between the glycogen-bound and soluble type 1 phosphatases would be investigated by using protein chemistry techniques. Synthetic phosphopeptides would be prepared to determine the minimal structural determinants for the action of phosphatases. The specificity of the native phosphatases towards various sites of glycogen synthase and possible role of site site interaction in the regulation of synthase phosphatase activity would be investigated. Glycogen synthase preparations containing 32P-phosphate in different sites would be prepared to investigate the role of site specific phosphatases in the activation of glycogen synthase in crude muscle extracts of normal and diabetic rabbits. Possible role of heat stable protein inhibitors and the regulatory subunit of cAMP-dependent protein kinase in the regulation of phosphatases would be investigated. The proposed investigation would advance our knowledge into the structure and regulation of phosphatases and would help understand the mechanism of slow activation of glycogen synthase in tissues of diabetic animals. The long term aim of the project is to understand the mechanism of activation of glycogen synthase by insulin.